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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .site-r>a {
            color: red;
        }

        .nav a {
            color: skyblue;
        }

        .nav,
        .sitenav {
            font: 14px 'Microsoft YaHei';
        }

        .nav>ul>li>a {
            color: green;
        }
    </style>
</head>

<body>
    <div class="nav">
        <ul>
            <li><a href="#">公司首页</a> </li>
            <li><a href="#">公司简介</a> </li>
            <li><a href="#">公司产品</a> </li>
            <li><a href="#">联系我们</a>
                <ul>
                    <li><a href="#">公司邮箱</a></li>
                    <li><a href="#">公司电话</a></li>
                </ul>
            </li>
        </ul>
    </div>
    <div class="sitenav">
        <div class="site-l">左侧侧边栏</div>
        <div class="site-r"><a href="#">登录</a></div>
    </div>
</body>
</html>